This invention relates to the field of intracorporeal medical devices such as guidewires for advancing intraluminal devices including stent delivery catheters, balloon dilatation catheters, atherectomy catheters and other intraluminal devices within a patient's body lumen.
Conventional guidewires for angioplasty, stent delivery, atherectomy and other vascular procedures usually comprise an elongated core member with one or more tapered sections near the distal end thereof and a flexible body such as a helical coil or a tubular body of polymeric material disposed about the distal portion of the core member. The flexible body may extend proximally to an intermediate portion of the guidewire. A shapeable member, which may be the distal extremity of the core member or a separate shaping ribbon which is secured to the distal extremity of the core member extends through the flexible body and is secured to the distal end of the flexible body by soldering, brazing or welding which forms a rounded distal tip. Torquing means are provided on the proximal end of the core member to rotate, and thereby steer, the guidewire while it is being advanced through a patient's vascular system.
Further details of guidewires, and devices associated therewith for various interventional procedures can be found in U.S. Pat. No. 4,748,986 (Morrison et al.); U.S. Pat. No. 4,538,622 (Samson et al.): U.S. Pat. No. 5,135,503 (Abrams); U.S. Pat. No. 5,341,818 (Abrams et al.); and U.S. Pat. No. 5,345,945 (Hodgson, et al.) which are hereby incorporated herein in their entirety by reference thereto.
In a typical coronary procedure using a guidewire, a guiding catheter having a preformed distal tip is percutaneously introduced into a patient's peripheral artery, e.g. femoral or brachial artery, by means of a conventional Seldinger technique and advanced and steered therein until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery.
There are two basic techniques for advancing a guidewire into the desired location within a patient's coronary anatomy through the in-place guiding catheter. The first is a preload technique which is used primarily for over-the-wire (OTW) catheters and the second is the bare wire technique which is used primarily for rail type catheters.
With the preload technique, a guidewire is positioned within an inner lumen of an OTW device such as a dilatation catheter or stent delivery catheter with the distal tip of the guidewire just proximal to the distal tip of the catheter and then both are advanced through the guiding catheter to the distal end thereof. The guidewire is first advanced out of the distal end of the guiding catheter into the patient's coronary vasculature until the distal end of the guidewire crosses the arterial location where the interventional procedure is to be performed, e.g. a lesion to be dilated or an arterial region where a stent is to be deployed. The catheter, which is slidably mounted onto the guidewire, is advanced out of the guiding catheter into the patient's coronary anatomy over the previously introduced guidewire until the operative portion of the intravascular device, e.g. the balloon of a dilatation or a stent delivery catheter, is properly positioned across the arterial location. Once the catheter is in position with the operative means located within the desired arterial location, the interventional procedure is performed. The catheter can then be removed from the patient over the guidewire. Usually, the guidewire is left in place for a period of time after the dilatation or stent delivery procedure is completed to ensure re-access to the distal arterial location if it is necessary. For example, in the event of arterial blockage due to dissected lining collapse, a rapid exchange type perfusion balloon catheter such as described and claimed in U.S. Pat. No. 5,516,336 (McInnes et al), can be advanced over the in-place guidewire so that the balloon can be inflated to open up the arterial passageway and allow blood to perfuse through the distal section of the catheter to a distal location until the dissection is reattached to the arterial wall by natural healing.
With the bare wire technique, the guidewire is first advanced by itself through the guiding catheter until the distal tip of the guidewire extends beyond the arterial location where the procedure is to be performed. Then a rapid exchange type catheter, such as described in U.S. Pat. No. 5,061,273 (Yock) and the previously discussed McInnes et al. patent, which are incorporated herein by reference, is mounted onto the proximal portion of the guidewire which extends out of the proximal end of the guiding catheter and which is outside of the patient. The catheter is advanced over the guidewire, while the position of the guidewire is fixed, until the operative means on the rapid exchange type catheter is disposed within the arterial location where the procedure is to be performed. After the procedure the intravascular device may be withdrawn from the patient over the guidewire or the guidewire advanced further within the coronary anatomy for an additional procedure.
An important attribute for guidewires is having sufficient radiopacity to be visualized under a fluoroscope, allowing the surgeon to advance the guidewire to a desired intraluminal location, particularly the distal extremity of the guidewire. Unfortunately, the most suitable materials for guidewires, such as stainless steel and NiTi alloys, exhibit relatively low radiopacity. Accordingly, various strategies have been employed to overcome this deficiency. Portions of the guidewire, usually the shapeable distal tip, are typically made from or coated with highly radiopaque metals such as platinum, iridium, gold or alloys thereof. For example, a 3 to 30 cm platinum tip-coil is frequently soldered to the distal extremity of the guidewire. An obvious drawback of these prior art methods is the high expense and scarcity of highly radiopaque metals and the difficulty and expense of manufacturing products from these materials. The requirement of both a high degree of radiopacity, high strength and flexibility can present design problems.
Accordingly, there remains a need for guidewires having sufficient radiopacity to allow visualization under a fluoroscope without the extensive use of expensive radiopaque metals such as platinum, gold, iridium and the like.